Electrodeposition of gold and gold alloys

ABSTRACT

ORGANO-PHOSPHORUS COMPOUNDS AND THEIR WATER SOLUBLE SALTS ARE INCORPORATED INTO AQUEOUS SOLUBLE CYANIDE GOLD OR GOLD ALLOY PLATING BATHS.

United States Patent Oflice 3,672,969 Patented June 27, 1972 US. Cl. 204-43 21 Claims ABSTRACT OF THE DISCLOSURE Organophosphorus compounds and their water soluble salts are incorporated into aqueous soluble cyanide gold or gold alloy plating baths.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of our previously filed application Ser. No. 830,547, filed June 4, 1969, now abandoned, which in turn is a continuation-in-part of application Ser. No. 634,134, filed Apr. 27, 1967, now abandoned, which in turn is a continuation-in-part of our earlier filed application Ser. No. 579,821, filed Sept. 16, 1966, now abandoned.

SUMMARY OF THE INVENTION This invention relates to electrodeposition of gold and gold alloys from an aqueous soluble cyanide gold plating bath in which there is dissolved an organo-phosphorus compound or its water soluble salt.

Organo phosphoric or phosphorus containing compounds can broadly be classified into two groups, namely, chelating and non-chelating. The organic-phosphorus chelating compounds can advantageously be used for the deposition of both pure gold and gold base alloys. The use of the non-chelating compounds produces good deposits of pure gold and particularly when used in combination with water soluble citrates. The use of these nonchelating organo-phosphorus compounds for electrodeposition of gold base alloys results in a bath having a limited plating range, usually around about one ampere per square foot, for bright deposits without the addition of a conventional chelating agent such as ethylene diamine tetraacetic acid.

The invention therefore broadly includes the addition or organo-phosphorus compounds to gold and gold alloy plating baths.

The invention further includes the addition of organophosphorus chelating agents or compounds to soluble gold plating baths for the deposition of pure gold and particularly gold alloys. The plating baths containing the or-gano-phosphorus chelating compounds not only provide the same operational advantages for the gold alloy plating process without the addition of the phosphates but produces gold base alloy deposits which are brighter even without the use of conventional brightening agents. To produce gold base alloys, various alloying metals as known in the art are added to the gold plating baths such as nickel, cobalt, iron, zinc and copper in the form of water soluble salts or metal chelates.

The invention further includes the addition of an organo-phosphorus compound or its water soluble salt in combination with a water soluble citrate to an aqueous gold plating bath for the electrodeposition of pure or 24 Karat gold. A synergistic reaction is obtained by use of this combination which substantially improves the plating range enabling the bath to operate at a higher rate of electrodeposition.

The plating baths of this invention may be effectively used over a wide range of pH depending upon the type of metal to be plated and the particular organo-phosphorus compound employed. If polyamine phosphonate compounds are employed [such as ethylenediaminetetra(methylphosphonic) acid or hexamethyldiaminetetra(methylphosphonic) acid] a pH of 12 or 13 and higher may be used. A pH as low as 2.5 or lower may be used with all of the organo-phosphorus compounds disclosed herein. For many plating processes, however, a pH of from 3 to 7.5 has been found to produce effective results. Operating the plating bath at a pH near neutrality or at a basic pH is advantageous for gold plating on base metals which bwozrlld be afiected or attacked by the acid in an acidic For particularly brilliant gold or gold alloy deposits, the organO-phosphOrus compound or its salt is used in combination with an amine such as those described in our US. Pat. No. 2,967,135. This process, which has all the advantages described hereinabove, is particularly suitable for the electrodeposition of 24 karat mirror bright gold plate up to and exceeding 0.0005 inch thick.

According to this invention, the process comprises electrodepositing gold or gold base alloys from an aqueous solution of at least one soluble gold cyanide salt in which there is dissolved from about 0.01 to 400 g./l. of an organo-phosphorus compound or its water soluble salt at a temperature in the range of between about 70 F. to F.

Examples of chelating organo-phosphorus compounds which can be used according to this invention include those conforming to the following structural formula:

wherein R is a lower alkylidene radical and their water soluble salts, R is hydrogen or a lower alkyl radical, and n is an integer from 1 to 3.

Some more specific examples of phosphonic acids coming within the above formula include those having the following structural formula:

and

wherein R contains 1 to 5 carbon atoms. We found aminotri(methy1phosphonic acid) to be eminently suitable for the present invention. This compound has the following structural formula:

N-[oH21' 0H)t]z Other phosphonic acids that can be used include aminotri(ethylidenephosphonic acid) and amino-tri(isopropylidene phosphonic acid).

Further examples of chelating organo-phosphorus compounds which can be used according to this invention include:

l-hydroxyethylidene-1,l diphosphonic acid ethylenediaminetetra (methylphosphonic) acid hexamethylenediaminetetra (methylphosphonic) acid hexamethyl phosphonic triamide s')2 ]a and Non-chelating organo-phosphorus compounds that can be used according to this invention include, benzene phosphonic acid, benzene phosphinic acid, ethyl acid phosphateC,H OPO(OH) and diethyl phosphite- (C,H O),'PHO.

The organo-phosphorus compounds can be used alone or in admixture with other orgauo-phosphorus compounds.

The soluble salts are the sodium salts and other alkali metal salts, such as potassium and lithium, as well as mixtures thereof. Ammoniumsalts and water soluble amine salts which exhibit the characteristics of the alkali metal salts may also be used.

The organo-phosphorus compounds containing -P=O can be referred to as phosphonyl compounds.

The organo-phosphorus compounds which give particularly good and improved results are the chelating compounds. The results of the non-chelating compounds tested to date can be classified as satisfactory.

The organo-phosphorus compounds, particularly the chelating compounds, when used in acidic gold plating baths substantially improve the plating characteristics of the bath. The resulting baths have excellent stability and are capable of operating at a wide temperature and pH range to provide lustrous fine grain and low porosity deposits, even for very thick deposits on the order of 0.0005 inch thick and above.

The pH of the plating bath when used without the soluble citrate is preferably maintained in the range between 3 and 5. The pH may be adjusted to the proper range by the addition of alkali metal hydroxide, preferably KOH, or an acid, preferably phosphoric acid.

The effectiveness of the organo-phosphorus compound in improving the electrodeposition of gold and gold alloys is not limited to any one particular aqueous gold plating Low metal, High metal, oz./gal. ozJgal.

Metallic gold, troy oz./gal. [as Kau(CN)2] 0 25 3 Di-potassium citrate 1. O

The addition of the organo-phosphorus compound to these baths substantially improves the plating range due to the synergistic action of the soluble citrate and the phosphonic acid as stated hereinabove. The amount of citrate used may be varied within the range of 1 to 400 g./l. depending on the number of process variables. The pH of such baths can be extended to a wider range by the addition of the organo-phosphorus compounds according to this invention to below pH 2.5 and about pH 13.

Modification of the gold cyanide bath that are used commercially for the production of bright gold and other gold base alloys are also found to be satisfactory for the process of this invention. We found that acid-gold bath to be eminently suitable. This type of bath contains alkali metal gold cyanide, an organic acid or its soluble salts, such as citric acid, ammonium citrate, sodium malate, and so forth.

In the brilliant gold deposits, as stated previously the organo-phosphorus compound preferably is added to the plating bath in combination with an amino compound. Suitable amines as disclosed in our previous patents include:

Ethylene diamine Diethylene triamine Triethylene tetramine I-Iydroxyethyl ethylene diamine Aminoethylethanolamine Monoethanolamine Triethanolamine Triisopropanoamine The amount of phosphonic acid to be added to the I plating bath depends on the process variables, alloying metals, gold concentrations, and others. In general, the

range of 0.01 to 400 g./l. work well for the electrodeposition of gold and gold base alloys. Further to illustrate this invention, specific examples are described hereinbelow:

EXAMIPLE I 24 karat lustrous gold deposits A suflicient amount of water is used to form one liter of solution in which there is dissolved 8 grams of potassium gold cyanide and 50 grams amino-tri(methylphosphonic acid) N[CH PO(0H) The pH of the solution is adjusted by the addition of potassium hydroxide to a pH about 4. The electrodeposition of gold is then carried out in a conventional manner at a temperature of about F. and a current density of 1 to 5 amperes per square foot. A lustrous, fine grain gold plate on brass base metal is obtained.

EXAMPLE H 24 karat lustrous gold deposits A sufiicient amount of water is used to form one liter of solution in which there is dissolved 8 grams of potassium gold cyanide, 80 grams amino-tri(methylphosphonic acid), and 90 grams potassium citrate. The pH of the solution is adjusted by the addition of potassium hydroxide to a pH about 6.0. The electrodeposition is then carried out in a conventional manner at a temperature about 145 F. and a current density of 1 to 5 amperes per square foot. A similar lustrous gold deposit is obtained.

EXAMPLE III Bright gold base alloy deposits A sufficient amount of water is used to form one liter of solution in which there is dissolved 4 grams of potassium gold cyanide, 150 grams of amino-tri(methylphosphonic acid), and 0.25 gram of cobalt as a water soluble salt. The solution is adjusted by the addition of potassium hydroxide to a pH of about 4.3 and the electrodeposition is carried out at a temperature of 100 F.

The current density may be varied in the range from 1 to about amperes per square foot. The resultant gold based alloy is bright and of excellent quality.

EXAMPLE IV Brilliant 24 karat gold deposits A gold plating bath in which there is dissolved 12 grams per liter of potassium gold cyanide, 150 grams per liter of amino-tri(methylphosphonic acid), and 25 grams per liter of tetraethylene pentamine is prepared. The pH of the solution is adjusted by the addition of potassium hydroxide to about 6 and the bath is permitted to age for approximately 10 days prior to electrodeposition. The electrodeposition of gold is carried out in a conventional manner at a temperature of about 140 F. and a current density of 1 to 2 amperes per square foot. A mirror bright 24 karat gold deposit is obtained.

The gold concentration suitable for the present application may vary from 1 gram per liter to 25 grams per liter, preferably in the range of 8 to 12 grams per liter. While the examples show the use of amino-tri(methylphosphonic acid), it is understood that other compounds falling within the scope of the claims may be used with beneficial results.

We claim:

1. A bath for producing deposits of gold or gold alloys by electrodeposition of gold or gold base alloys comprising an aqueous solution containing at least one soluble gold cyanide compound in an amount eifective to produce electrodeposits of pure gold, or gold alloys when a codepositable base metal is also present, and a Water soluble organo-phosphorus chelating agent or a water soluble organo-phosphorus non-chelating compound comprising phenyl phosphonic acid or phenyl phosphinic acid or ethyl acid phosphate or diethyl phosphite, or a water soluble salt of said chelating agent or non-chelating compounds in an amount above about 0.01 g./l.

2. A bath for producing deposits of gold or gold alloys by electrodeposition of gold or gold alloys comprising an aqueous solution containing at least one soluble gold cyanide compound in an amount effective to produce electrodeposits of pure gold, or gold alloys when a co-depositable base metal is also present, and an organo-phosphorus chelating agent, or a water soluble salt of said chelating agent in an amount above about 0.01 g./l.

3. The bath of claim 2 in which the chelating agent is l-hydroxy-ethylidene-l, l-diphosphonic acid or its water soluble salts.

4. The bath of claim 3 which also contains an amine brightening agent.

5. The bath of claim 3 which contains a water soluble citrate salt in sufiicient amount to improve the gold or gold alloy plating.

6. The bath of claim 2 in which the organo-phosphorus chelating agent is a monoamine or poly-amine phosphonic acid compound or a lower alkyl derivative thereof, or its water soluble salt.

7. The bath of claim 2 in which'the phosphorus chelating agent is an alkyl amine tetra (alkyl phosphonic) acid or its water soluble salt.

8. The bath of claim 2 in which the organo-phosphorus agent is ethylenediamine tetramethylphosphonic acid or its water soluble salts.

9. The bath of claim 2 in which the organo-phosphorus agent is he'xamethylenediamine tetramethylphosphonic acid or its water soluble salts.

10. The bath of claim 2 in which the organo-phosphorus agent is hexamethyl phosphonic tn'amide or its water soluble salts.

11. The bath of claim 2 in which theo rgano-phosphorus agent conforms to the structural formula:

or its water soluble salts.

12. The bath of claim 2 in which the organo-phosphorus agent conforms to the structural formula:

in which R is a lower alkylidene radical, R is hydrogen or a lower alkyl radical and n is an integer from 1 to 3 or its water soluble salts.

13. The bath of claim 2 in which the chelating agent is anliino-tri (methylphosphonic acid), or its water soluble sa ts.

14. The bath of claim 2 which contains an amine brightening agent.

15. The bath of claim 2 which contains a water soluble citrate in suificient amount to improve the gold or gold alloy plating.

16. A bath for producing gold or gold alloys by electrodeposition of gold or gold alloys comprising an aqueous solution containing at least one soluble gold cyanide compound in an amount effective to produce electrodeposits of pure gold, or gold alloys when a co-depositable base metal is also present, and non-chelating phenyl phosphonic acid or phenyl phosphinic acid or ethyl acid phosphate or diethyl phosphite or their water soluble salts in an amount above about 0.01 g./l.

17. The bath of claim 16 in which the non-chelating agent is ethyl acid phosphate.

18. The bath of claim 16 in which the non-chelating agent is diethyl phosphite.

19. The bath of claim 16 which contains a soluble citrate in a sufficient amount to improve the quality of the gold or gold alloy plating.

20. The bath of claim 16 which contains an amine brightening agent in a sufiicient amount to improve the brightness of the gold or gold alloy plating.

21. A process for the electrodeposition of gold or gold base alloys which comprises the steps of electrolyzing said gold or gold base alloy metal from a bath containing at least one soluble gold cyanide compound in an amount sufiicient to produce electrodeposits of pure gold, or gold alloys when a co-depositable base material is also present in the bath, and a water soluble organo-phosphorus chelating agent or a water soluble organo-phophorus nonchelating compound comprising phenyl phosphonic acid or phenyl phosphinic acid or ethyl acid phosphate or di- 7 8 ethyl phosphite, or a water soluble salt of said chelating 2,606,902 8/1952 Parker et a1. 260-239 EP agents or non-chelating compounds in an amount above 2,724,687 11/1955 Spfeter et 204-43 about 01 2,760,974 8/1956 McKinnis 260 -551 PX 2,892,760 6/1959 Giindel et al. 204-44 5 2,905,601 9/1959 Rinker et a1. 204-43 References 22 NT 3,104,212 9/1963 Rinker et a1. 204-46 UNITED STATES TE S FOREIGN PATENTS 2,967,135 1/1961 OStlOW et al. 20443 960 314 /19 4 Great i i 204 4 3,084,111 4/1963 Strauss et al. 204-51 2,599,807 6/1952 Bersworth 260502.5 GERALD L. KAPLAN, Primary Examiner 2,841,611 7/1958 Bersworth 260-502.5 3,475,293 10/1969 'Haynes et a1 204'48 C1.

3,380,898 4/1968 Danemark et al. 204--44 20444, 46; 26023-9 EP, 551 P (5/69) I \1 l vr 1" '1 r W O M-1 7 3 gill illiCATib O1 CQRLULCTlGN Patent No. 3 Dated June 27, 19-72 Immntoflg) FRED I NOBEL and BARNET D. OSTROW It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 16 "2,5 'pH 13'' should read -2,5 and above pH l3--.

Column 6, line 7l "base material" should read base metal--.

Signed and sealed this 6th day of March 1973 (SEAL) Attest:

EDWARD M. FLETCHER JR Atteqti ROBERT GOTTSCHALK ng )fflcer Commissioner of Patents 

